IP Pool Sharing
Protocol

This chapter
provides information on configuring an enhanced, or extended, service. The
product administration guides provide examples and procedures for configuration
of basic services on the system. It is recommended that you select the
configuration example that best meets your service model, and configure the
required elements for that model before using the procedures in this chapter.

Overview

The IP Pool
Sharing Protocol (IPSP) is a protocol that system-based
HA services can use during an offline-software upgrade
to avoid the assignment of duplicate IP addresses to sessions while
allowing them to maintain the same address, and to preserve
network capacity.

In order for IPSP
to be used, at least two system-based HAs with identical
configurations must be present on the same LAN. IPSP uses
a primary & secondary model to manage the IP pools between the
HAs. When used, this protocol ensures the following:

In-progress
sessions can be handed-off to the secondary HA when an
offline-software upgrade is being performed on the primary
and receive the same IP address that it was originally assigned.

New sessions can be
redirected to the secondary HA when an offline-software
upgrade is being performed on the primary and receive a non-duplicate
IP address.

The protocol is enabled
at the interface level. Each system-based HA must
have an IPSP-enabled interface configured in the same context
as the HA service for this protocol to function properly.

Primary HA Functionality

The primary
HA is the system that is to be upgraded. It performs the
following functions for IPSP:

Queries the pool information
from the secondary HA the pool configurations on both
HAs must be identical

Assigns an IP address
or address block to the secondary HA when requested by the secondary
HA the primary HA releases sessions if they have an IP
address requested by the secondary

For graceful termination
conditions (e.g. an administrative user
issues the reload command), sends
a termination message to the secondary HA causing it to assume the
responsibilities of the primary HA until the primary is available again.

Sends a trap when
the number of calls drops to zero after starting IPSP

Secondary HA Functionality

The secondary
HA is the system that takes over Mobile IP sessions from the primary
HA that is being upgraded. It performs the following functions
for IPSP:

Locks the IP pools
until it receives an address or address block assignment from the
primary HA it unlocks the IP pools after busying out the addresses
that are not assigned to it

Processes address
requests for sessions that are within the address block assigned
to it

Communicates with
the primary HA, as needed, to request IP addresses
that are not currently assigned to it it does not assign
the address until the primary HA approves it

For graceful termination
conditions (e.g. an administrative user
issues the reload command), it
notifies the primary HA that it is going out of service

Assumes the responsibility
of the primary HA when requested to

In the event that
it determines that primary HA is not available, it assumes
the responsibility of the primary HA if there is at least one address
allocated to verify that the AAA server is re-configured
to direct the calls

Requirements, Limitations, &
Behavior

One IPSP interface
can be configured per system context.

The IPSP interfaces
for both the primary and secondary HAs must be configured to communicate
on the same network.

If IP pool busyout
is enabled on any configured address pool, IPSP can not
be configured.

The IP pool configuration (pool
name, addresses, priority, pool group, etc.) on
both the HAs must be identical.

IP pools cannot be
modified on either the primary or the secondary HAs once IPSP is enabled.

Sessions are dropped
during the IPSP setup process if:

the primary HA has
not yet approved an IP address or address block.

the primary HA is
not known to the secondary HA.

Once an address is
assigned to the secondary HA, all the information about
that address is erased on the primary HA and that address becomes
unusable by the primary HA.

LRU is not supported
across the systems. Although, LRU continues to
be supported within the system.

If the IPSP configuration
is not disabled before removing the HA from the IPSP network link, sessions
may be rejected if the system's VPN Manager is rebooted
or restarts.

IPSP does not control
static IP pools. An external application (AAA, etc.) must
be responsible for ensuring that duplicate addresses are not assigned.

IPSP ignores interface
failures allowing the configured dead-interval timer to determine
when the HA should become the primary and control the pool addresses. Before
the dead-interval timer starts, the secondary
HA maintains its state and any busied out addresses remain busied
out. After the dead-interval timer starts, IPSP
marks the neighboring peer HA as down, becomes primary, and
will unbusy out all pool addresses.

How IPSP Works

IPSP operation
requires special configuration in both the primary and secondary
HAs. As mentioned previously, both HAs must have
identical configurations. This allows the secondary HA
to process sessions identically to the primary when the primary
is taken offline for upgrade.

Configuration must
also be performed on the AAA server. Whereas subscriber
profiles on the AAA server originally directed sessions to the primary
HA, prior to using IPSP, subscriber profiles must
be re-configured to direct sessions to the secondary HA.

There are two scenarios
in which IPSP takes effect:

New sessions: Once
IPSP is configured, new sessions are directed to a secondary
HA (HA2) allowing the primary HA to go through
a software upgrade without degrading network capacity. The
secondary HA requests addresses from the primary HA's (HA1) pools
as needed. As the addresses are allocated, they
are busied out on the primary HA. This procedure is displayed
below.

Session handoffs: Once
IPSP is configured, sessions originally registered with
the primary HA (HA1) are re-registered
with the secondary HA (HA2). To ensure
the session is assigned the same IP address, the secondary
HA requests the address from the primary HA. The primary
HA verifies the binding and releases it to the secondary HA which, in
turn, re-assigns it to the session. As
the addresses are allocated, they are busied out on the
primary HA. This procedure is displayed below.

IPSP Operation for
New Sessions

The following figure
and text describe how new sessions are handled when IPSP is enabled.

Figure 1. IPSP Operation for New Sessions

Table 1 IPSP Operation
for New Sessions Description

Step

Description

1

A mobile node (MN) attempting to establish a data session is
connected to PDSN/FA 2.

2

PDSNFA 2 authenticates the subscriber with the AAA server. One
of the attributes returned by the AAA server as part of a successful
authentication is the IP address of the secondary HA.

3

PDSN/FA 2 forwards the session request to HA2 for processing.
HA2 processes the session as it would for any Mobile IP session.

4

With IPSP enabled, prior to assigning an IP address, HA2 sends a
request to HA1 for an IP address.

5

HA1 allocates the address to HA2 and busies it out so it can not
be re-assigned.

6

HA1 responds to HA2 with the IP address for the session.

7

HA2 proceeds with session processing and provides PDSN/FA 2 with
the IP address for the MN.

8

The MN and PDSN/FA 2 complete session processing.

IPSP Operation for
Session Handoffs

The following figure
and text describe how session handoffs are handled when IPSP is enabled.

Figure 2. IPSP Operation for Session Handoffs

Table 2 IPSP Operation
for Session Handoffs Description

Step

Description

1

A mobile node (MN) is connected to PDSN/FA 1.

2

The MN's session is handed-off to PDSN/FA2 and goes through the
re-registration process.

3

PDSN/FA 2 authenticates the subscriber with the AAA server as
part of the re-registration process. One of the attributes returned by the AAA
server as part of a successful authentication is the IP address of the
secondary HA.

4

PDSN/FA 2 forwards the session request to HA2 for processing.
Included in the request is the MN's current IP address.

5

With IPSP enabled, prior to assigning an IP address, HA2 sends a
request to HA1 for an IP address.

6

HA1 verifies the MN's information and releases the binding. It
then busies out the address so it can not be re-assigned.

7

HA1 allocates the original IP address to HA2 for the session.

8

HA2 proceeds with session processing and provides PDSN/FA 2 with
the IP address for the mobile node.

9

The mobile node and PDSN/FA 2 complete session processing.

Configuring IPSP
Before the Software Upgrade

Configuring IPSP
requires changes to the primary HA (the HA on which the software upgrade is to
occur), the secondary HA (the HA to which subscribers sessions are to be
directed), and the AAA server.

This section
provides information and instructions for configuring IPSP before the software
upgrade.

Important:

This section
provides the minimum instruction set for configuring IPSP on the system. For
more information on commands that configure additional parameters and options,
refer to the
IPSP
Configuration Mode Commands
chapter in the
Command Line
Interface Reference.

Verify your ACL
configuration by following the steps in the
Verifying the
IPSP Configuration section.

Step 7

Proceed for
software upgrade as described in Off-line Software Upgrade section in the
System
Administration Guide.

Step 8

Save your
configuration to flash memory, an external memory device, and/or a network
location using the Exec mode command
save
configuration. For additional information on how to verify and
save configuration files, refer to the
System
Administration Guide and the Command Line Interface Reference.

Configuring the
AAA Server for IPSP

For subscriber
session establishment, the AAA server provides the IP address
of the HA that is to service the session. This information
exists in the 3GPP2_MIP_HA_Address RADIUS
attribute configured for the subscriber.

Because the primary
HA has been responsible for facilitating subscriber sessions, its
IP address is the one configured via this attribute. For
IPSP however, the attribute configuration must change in
order to direct sessions to the secondary HA.

To do this, reconfigure
the 3GPP2_MIP_HA_Address RADIUS attribute
for each subscriber on the AAA server with the IP address of the
secondary HA.

The precise instructions
for performing this operation vary depending on the AAA server vendor. Refer
to the documentation for your AAA server for more information.

Enabling IPSP on
the Secondary HA

The secondary
HA is the alternate HA that is to take responsibility while the
primary HA is upgraded.

Important:

This section provides
the minimum instruction set for configuring IPSP on the system. For
more information on commands that configure additional parameters
and options, refer to the IPSP Configuration
Mode Commands chapter in the Command Line Interface Reference.

The interface must
be configured in the same context as the HA service and must be
on the same network as the primary HA's IPSP interface.

ipsp_if_name is
the name of the interface on which you want to enable IPSP.

dead-interval
is an optional command to configure time to wait before retrying
the primary HA for the IP Pool Sharing Protocol.

Enabling IPSP on
the Primary HA

The primary
HA is the HA that is to be upgraded.

Important:

This section provides
the minimum instruction set for configuring IPSP on the system. For
more information on commands that configure additional parameters
and options, refer to the IPSP Configuration
Mode Commands chapter in the Command Line Interface Reference.

The interface must
be configured in the same context as the HA service and must be
on the same network as the secondary HA's IPSP interface.

ipsp_if_name is
the name of the interface on which you want to enable IPSP.

dead-interval
is an optional command to configure time to wait before retrying
the secondary HA for the IP Pool Sharing Protocol.

Important:

Once this configuration
is done, the primary HA begins to hand responsibility for
sessions and release IP addresses to the secondary HA. Prior
to performing the software upgrade, all IP addresses must
be released. When IPSP has released all IP pool addresses
from the primary HA an SNMP trap (starIPSPAllAddrsFree) is
triggered.

Verifying the IPSP
Configuration

These instructions
are used to verify the IPSP configuration.

Verify that IPSP has
released all IP addresses by entering the following command in Exec
Mode with in specific context:

show ip ipsp

The
output of this command provides the list of used addresses and released
addresses. The system will send the starIPSPAllAddrsFree trap
once all IP addresses are released. When the value in the Used Addresses column
reaches 0 for all IP pools listed, then the primary HA
sends the SNMP trap and notifies the secondary HA to take over as
the primary HA.

Configuring IPSP
After the Software Upgrade

If desired, IP pool
addresses can be migrated from the original secondary HA back to the original
primary HA once the upgrade process is complete.

Important:

It is important to
note that the HA that was originally designated as the secondary is now
functioning as the primary HA. Conversely, the HA that was originally
designated as the primary is now functioning as the secondary.

In order to migrate
the addresses, both HAs and the AAA server must be configured according to the
instructions in this section.

This section
provides information and instructions for configuring IPSP after the software
upgrade.

Important:

This section
provides the minimum instruction set for configuring IPSP on the system. For
more information on commands that configure additional parameters and options,
refer
IPSP
Configuration Mode Commands
chapter in the
Command Line
Interface Reference.

Verify your ACL
configuration by following the steps in the
Verifying the
IPSP Configuration.

Step 6

Save your
configuration to flash memory, an external memory device, and/or a network
location using the Exec mode command
save
configuration. For additional information on how to verify and
save configuration files, refer to the
System
Administration Guide and the Command Line Interface Reference.

Disabling IPSP

Once all IP
addresses on the primary HA have been released, IPSP must
be disabled on both the primary and secondary HAs.

Caution

Prior to disabling
IPSP, ensure that the primary HA has released all IP addresses
to secondary HA.

Follow the instructions
in this section to disable IPSP on primary and secondary HA after migration
of all IP addresses.

Important:

This section provides
the minimum instruction set for disabling IPSP on the HAs. For
more information on commands, refer to the IPSP Configuration
Mode Commands chapter in the Command Line Interface
Reference.